The present invention relates to a negative working chemical amplification type resist composition which is used for forming: a resist pattern by irradiation of radiation such as ultra violet ray, electron beam or X-rays and by alkaline development, and for manufacturing semiconductor integrated circuits.
Negative working chemical amplification type resists comprising an alkali-soluble resin, a cross-linking agent and an acid generator are alkali-soluble as they are, but are changed to an alkali-insoluble state by cross-linking the alkali-soluble resin with the cross-linking agent through the post exposure bake (sometimes abbreviated as PEB) with the aid of an acid, working as a catalyst, generated from the acid generator by irradiation with a radiation. Therefore, these resists can form a negative image by irradiation with a radiation through a mask (so-called patterning exposure) and alkaline development. These negative working chemical amplification type resists have frequently been used in the production of integrated circuits because of their excellent resolution and sensitivity. As the recent increase in integration level of the integrated circuits, a further improvement in the resolution has been demanded.
The alkali-soluble resin which have been used in conventional known negative working chemical amplification type resists were novolak resins, polyvinylphenol, and polyvinylphenol compounds in which hydroxyl groups are partially alkyl etherified, as disclosed in JP-A-7-295220. A sufficient and satisfactory resolution for meeting the recent demand, however, could not be obtained by simply improving the alkali-soluble resin.
The purpose of the present invention is to provide negative working chemical amplification type resist compositions having an improved resolution. As the result of extensive studies for attaining such purpose, the present inventors have found the fact that the resolution can be further improved by comprising a certain specific compound together with an alkali-soluble resin, a cross-linking agent and an acid generator. The present invention has been completed based on such fact.
The present invention provides a negative working chemical amplification type resist composition comprising an alkali-soluble resin; a cross-linking agent; a N-substituted succinimide compound represented by the owing formula (I): 
wherein R represents an unsubstituted or substituted alkyl, an alicyclic hydrocarbon residue, an aryl or a camphor group, and;
an acid generator other than the above N-substituted succinimide compound.
The alkali-soluble resin and the cross-linking agent in the present invention may be those commonly used in this field. As the alkali-soluble resin, a novolak resin, polyvinylphenol or a polyvinylphenol compound in which hydroxyl groups are partially alkyl etherified is commonly used.
A novolac resin can usually be obtained by condensing a phenol compound and an aldehyde in the presence of an acid catalyst.
Examples of the phenol compound used in the preparation of the novolac resin include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,5-xylenol, 3,4-xylenol, 3,5-xylenol, 2,3,5-trimethylphenol, 2-tert-butylphenol, 3-tert-butylphenol, 4-tert-butylphenol, 2-tert-butyl-4-methylphenol, 2-tert-butyl-5-methylphenol, 2-methylresorcinol, 4-methylresorcinol, 5-methylresorcinol, 2-methoxyphenol, 3-methoxyphenol, 4-methoxyphenol, 2,3-dimethoxyphenol, 2,5-dimethoxyphenol, 3,5-dimethoxyphenol, 2-methoxyresorcinol, 4-tert-butylcatechol, 2-ethylphenol, 3-ethylphenol, 4-ethylphenol, 2,5-diethylphenol, 3,5-diethylphenol, 2,3,5-triethylphenol, 2-naphthol, 1,3-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,7-dihydroxynaphthalene and a polyhydroxytriphenylmethane compound obtainable by condensation of xylenol and hydroxybenzaldehyde. These phenol compounds can be used singly or in combination of two or more.
Examples of the aldehyde used in the preparation of the novolac resin include aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde, iso-butylaldehyde, pivalaldehyde, n-hexylaldehyde, acrolein and crotonaldehyde; alicyclic aldehydes such as cyclohexanealdehyde, cyclopentanealdehyde, furfural and furylacrolein; aromatic aldehydes such as benzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, p-ethylbenzaldehyde, 2,4-dimethylbenzaldehyde, 2,5-dimethylbenzaldehyde, 3,4-dimethylbenzaldehyde, 3,5-dimethylbenzaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, o-anisaldehyde, m-anisaldehyde, p-anisaldehyde and vanillin; and aromatic-aliphatic aldehydes such as phenylacetaldehyde and cinnamaldehyde. These aldehydes can be used singly or in combination of two or more. Among these aldehydes, formaldehyde is preferably used because of easy availability in the industry.
Examples of the acid catalyst used for condensation of the phenol compound with the aldehyde compound include inorganic acids such as hydrochloric acid, sulfuric acid, perchloric acid and phosphoric acid; organic acids such as formic acid, acetic acid, oxalic acid, trichloroacetic acid and p-toluenesulfonic acid; and bivalent metal salts such as zinc acetate, zinc chloride and magnesium acetate. These acid catalysts can be used singly or in combination of two or more. The condensation reaction can be carried out according to the usual manner, for example, at a temperature within a range of 60 to 120xc2x0 C. for 2 to 30 hours.
It is preferred for improving the resolution of the resist that a novolak resin having a weight average molecular weight of 900 or less is contained as a part of the alkali-soluble resin. The weight average molecular weight herein refers to a value measured by gel permeation chromatography (GPC) using polystyrene as the standard. This is also applied to other weight average molecular weight referred to below in this specification. These low molecular weight novolak resin oligomer can also be produced by condensing a phenol compound as described above and an aldehyde in the presence of an acid catalyst according to the conventional method. In this reaction, reaction conditions for obtaining low molecular weight product should be adopted. For example, amount of acid should be smaller, such as about 0.001 to 0.01 times the mole of the phenol compound as the raw material, and reaction period should be shorter such as about 1 to 5 hours.
When the low molecular weight novolak resin oligomer is used as a part of the alkali-soluble resin, the rest of the alkali-soluble resin is preferably a resin having a greater weight average molecular weight than said resin. For example, a resin having a weight average molecular weight of 2,000 or more is preferable. Particularly, co-use of a novolak resin mainly comprising a higher molecular weight fraction is preferred for improving the resolution. Specifically, it is preferred that a pattern area of the resin corresponding to polymers having a, molecular weight of 1,000 or less is 25% or less, more preferably 20% or less, of the total pattern area except for the area of the unreacted phenol compound as the raw material. The pattern area herein refers to an area measured by GPC with an UV detector at 254 nm. The molecular weight herein refers to a value measured using polystyrene as the standard, as in the weight average molecular weight described above. The novolak resin mainly comprising a higher molecular weight fraction as described above can be produced, for example, by applying a fractionation to a novolak resin obtained by the condensation reaction. For carrying out the fractionation, adoptable methods include: a method in which a novolak resin is dissolved in a good solvent, and then the solution is poured into water for precipitating the higher molecular weight fraction; and a method in which said solution is mixed with a poor solvent such as pentane, hexane or heptane, and the lower layer containing mainly the higher molecular weight fraction is separated. Examples of the good solvent include alcohols such as methanol and ethanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, glycol ethers such as ethyl cellosolve, glycol ether esters such as ethyl cellosolve acetate, ethers such as tetrahydrofuran, or else. It is preferred that the novolak resin mainly comprising a higher molecular weight fraction has a weight average molecular weight of 5,000 or more, particularly 6,000 or more.
Polyvinylphenol and its partially alkyl-etherified product can also be used as an alkali-soluble resin. These can be co-used with a novolak resin. While positional relation between the vinyl group and the hydroxyl group in the vinylphenol as the constituent of polyvinylphenol is not particularly limited, usually the vinyl group is at the para-position of the hydroxyl group. Polyvinylphenol can be produced, for example, by hydrolyzing poly(tert-butoxystyrene) obtained by polymerization of tert-butoxystyrene. Products having various average molecular weights and molecular weight distributions are commercially available and these commercial products can be used.
It is more preferable for improving resolution to use a polyvinylphenol in which hydroxyl groups are partially alkyl etherified. Examples of methods for obtaining partially alkyl-etherified polyvinylphenol include a method in which polyvinylphenol and an alkyl halide are reacted in the presence of an alkali such as potassium carbonate or sodium carbonate as described in JP-A-7-295220. Alkyls as constituents of the alkyl ethers may be those having about 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl and butyl. The rate of alkyl ether (alkyl-etherified rate) among the hydroxyl groups in polyvinylphenol is generally up to about 35% by mole and preferably 10% by mole or more.
The cross-linking agent may be anyone that results cross-linking of the alkali-soluble resin such as a novolak resin or polyvinylphenol. Examples thereof include epoxy compounds, compounds having a methylol group and compounds having a methylol alkyl ether group. Epoxy cross-linking agents are generally a lower molecular weight phenol compound such as Bisphenol A or an oligomer of novolak resin in which the phenolic hydroxyl is converted to glycidyl ether.
Examples of cross-linking agents having a methylol group or a methylol alkyl ether group include melamine compounds and guanamine compounds represented by the following formula (II): 
wherein R1 represents a group: xe2x80x94NR6R7 or an aryl, at least one of R2, R3, R4, R5, R6 and R7 independently represents a group of xe2x80x94CH2OR , wherein R8 represents hydrogen or an alkyl, and the rest of R2, R3, R4, R5, R6 and R7 represent hydrogen. The aryl is typically phenyl, 1-naphthyl or 2-naphthyl. These phenyl and naphthyls may have a substituent such as an alkyl, an alkoxy and a halogen. The alkyl and alkoxy may have about 1 to 6 carbon atoms. The alkyl represented by R8 is generally methyl or ethyl, in particular methyl.
Examples of the melamine compounds represented by the formula (II), i.e. compounds of the following formula (III): 
wherein R2, R3, R4, R5, R6 and R7 are as defined above, include hexamethylol melamine, pentamethylol melamine, tetramethylol melamine, hexamethoxymethyl melamine, pentamethoxymethyl melamine, tetramethoxymethyl melamine and hexaethoxymethyl melamine. Examples of the guanamine compounds represented by the formula (II), i.e., compounds of the formula (II) wherein R1 is an aryl, include tetramethylol benzoguanamine, tetramethoxymethyl benzoguanamine, trimethoxymethyl benzoguanamine and tetraethoxymethyl benzoguanamine.
In addition to the above, compounds having a methylol group or a methylol alkyl ether group such as those listed below can also be used as the cross-linking agents:
(a) 2,6-bis(hydroxymethyl)-4-methylphenol,
(b) 4-tert-butyl-2,6-bis(hydroxymethyl) phenol,
(c) 5-ethyl-1,3-bis(hydroxymethyl)perhydro-1,3,5-triazine-2-one (common name: N-ethyldimethyloltriazone) or its dimetyl ether,
(d) dimethylol trimethyleneurea or its dimethyl ether,
(e) 3,5-bis(hydroxymethyl)perhydro-1,3,5-oxadiazine-4-one (common name: N-dimethylolurone) or its dimetyl ether,
(f) tetramethylol glyoxal diureine or its tetramethyl ether. 
and compounds of (c) to (f), in which the methyl group is substituted by another alkyl group.
In the compositions of the present invention, a N-substituted succinimide compound represented by the above formula (I) and an acid generator other than it are additionally comprised together with the alkali-soluble resin and the cross-linking agent described above.
In the formula (I), R is a sulfonic acid residue and may specifically be an alkyl, an alicyclic hydrocarbon residue, an aryl or a camphor group. The alkyl here may be unsubstituted or substituted. It may have about 1 to 10 carbon atoms. When it has 3 or more carbon atoms, it may be a straight chain or a branched chain. Examples of the groups which may be a substituent on the alkyl include an alkoxy, a halogen, nitro, an alicyclic hydrocarbon residue and an aryl. The alkoxy as the substituent on the alkyl may have about 1 to 4 carbon atoms. Examples of halogen include fluorine, chlorine and bromine. The alicyclic hydrocarbon residue represented by R or the alicyclic hydrocarbon residue as a substituent on the alkyl represented by R refers to a monovalent group which has an alicyclic ring having a single bond for connecting another group, and may have about 5 to 12 carbon atoms. Typical alicyclic hydrocarbon residue includes cycloalkyls and specifically cyclopentyl, cyclohexyl, methylcyclohexyl and the like. The aryl represented by R or aryl as a substituent on alkyl represented by R refers to a monovalent group which has an aromatic ring having a single bond for connecting another group. Typical aryl includes phenyl, naphthyl and the like. These aromatic rings such as phenyl, naphthyl and the like may be unsubstituted or substituted. Examples of the groups which may be a substituent on the aryl include an alkyl having about 1 to 4 carbon atoms, an alkoxy having about 1 to 4 carbon atoms and a halogen such as fluorine, chlorine and bromine, nitro. Examples of the alkyl substituted with an aryl, such group can be called as an aralkyl, include benzyl and phenethyl. Camphor group represented by R refers to a monovalent group derived from camphor. In particular, 10-camphor group, i.e., a group formed by removing the sulfonic acid group from 10-camphorsulfonic acid, is preferred.
Specific examples of N-substituted succinimide compound represented by the formula (I) include the following compounds:
N-(ethylsulfonyloxy)succinimide,
N-(isopropylsulfonyloxy)succinimide,
N-(butylsulfonyloxy)succinimide,
N-(hexylsulfonyloxy)succinimide,
N-(trifluoromethylsulfonyloxy)succinimide,
N-(chloromethylsulfonyloxy)succinimide,
N-(cyclohexylmethylsulfonyloxy)succinimide,
N-(benzylsulfonyloxy)succinimide,
N-(cyclohexylsulfonyloxy)succinimide,
N-(phenylsulfonyloxy)succinimide,
N-(p- or o-tolylsulfonyloxy)succinimide,
N-(2,5-xylylsulfonyloxy)succinimide,
N-(4-ethylphenylsulfonyloxy)succinimide,
N-(2,4,6-trimethylphenylsulfonyloxy)succinimide,
N-(2,4,6-triisopropylphenylsulfonyloxy)succinimide,
N-(4-methoxyphenylsulfonyloxy)succinimide,
N-(4-chlorophenylsulfonyloxy)succinimide,
N-(2,4,5-trichlorophenylsulfonyloxy)succinimide,
N-(2- or 4-nitrophenylsulfonyloxy)succinimide,
N-(4-methoxy-2-nitrophenylsulfonyloxy)succinimide,
N-(1-naphthylsulfonyloxy)succinimide,
N-(10-camphorsulfonyloxy)succinimide, and the like.
N-substituted succinimide compound of the formula (I) acts as an acid generator in far ultraviolet rays exposure, electron beams exposure, X-ray exposure and the like, but is not sensitive to a light having a wavelength of 300 nm or above, such as i-ray having a wavelength of 365 nm. In order to have sensitivity to a light having such a longer wavelength, an acid generator sensitive to a radiation having such a wavelength, such as an oxime acid generator described in JP-A-9-222725, is added. Preferred acid generators for using in combination with N-substituted succinimide compound of the formula (I) include oxime sulfonate compounds represented by the following formula (IV): 
wherein R11 represents an unsubstituted or substituted alkyl, an alicyclic hydrocarbon residue, an aryl or a camphor group, and R12, R13 and R14 independently represent hydrogen, a halogen, an alkyl, an alkoxy or an alkyl-substituted amino.
R11 in the formula (IV) is also a sulfonic acid residue. Groups similar to those described above in connection with R in the formula (I) may be R11 in the formula (IV). In addition, R12, R13 and R14 in the formula (IV) are substituents on phenyl and may be hydrogen, a halogen, an alkyl, an alkoxy or an alkyl-substituted amino, respectively. The halogen here includes fluorine, chlorine, bromine and so on. The alkyl and alkoxy may have about 1 to 4 carbon atoms, respectively. The alkyl-substituted amino may be monoalkylamino or dialkylamibno, wherein the alkyl may have about 1 to 6 carbon atoms.
Examples of the oxime sulfonate compound represented by the formula (IV) include compounds listed below by chemical names or the corresponding structural chemical formula:
(IVa) xcex1-(hexylsulfonyloxyimino)-4-methoxybenzyl cyanide,
(IVb) xcex1-(trifluoromethylsulfonyloxyimino)-4-methoxybenzyl cyanide,
(IVc) xcex1-(p-tolylsulfonyloxyimino)-4-methoxybenzyl cyanide,
(IVd) xcex1-(1-naphthylsulfonyloxyimino)-4-methoxybenzyl cyanide,
(IVe) xcex1-(2-naphthylsulfonyloxyimino)-4-methoxybenzyl cyanide,
(IVf) xcex1-(p-tolylsulfonyloxyimino)-4-diethylamino benzyl cyanide,
(IVg) xcex1-(p-tolylsulfonyloxyimino)-3,4-dimethoxybenzyl cyanide. 
Even when exposure to far ultraviolet rays, electron beams, X-rays and the like to which the N-substituted succinimide compound of the formula (I) is sensitive is adopted, it is preferable to add another acid generator for enhancing the sensitivity of the resist. Examples of such acid generator sensitive to far ultraviolet rays, electron beams, X-rays or the like include onium salt compounds, organic halogen compounds, particularly haloalkyl-s-triazine compounds, sulfone compounds and sulfonate compounds. Specific examples include the following compounds:
(1) Onium Salt Compounds:
diphenyliodonium trifluoromethanesulfonate,
4-methoxyphenylphenyliodonium hexafluoroantimonate,
4-methoxyphenylphenyliodonium trifluoromethanesulfonate,
bis(4-tert-butylphenyl)iodonium tetrafluoroborate,
bis(4-tert-butylphenyl)iodonium hexafluorophosphate,
bis(4-tert-butylphenyl)iodonium hexafluoroantimonate,
bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate,
triphenylsulfonium hexafluorophosphate,
triphenylsulfonium hexafluoroantimonate,
triphenylsulfonium trifluoromethanesulfonate,
4-methoxyphenyldiphenylsulfonium hexafluoroantimonate,
4-methoxyphenyldiphenylsulfonium trifluoromethanesulfonate,
p-tolyldiphenylsulfonium trifluoromethanesulfonate,
2,4,6-trimethylphenyldiphenylsulfonium trifluoromethanesulfonate,
4-tert-butylphenyldiphenylsulfonium trifluoromethanesulfonate,
4-phenylthiophenyldiphenylsulfonium hexafluorophosphate,
4-phenylthiophenyldiphenylsulfonium hexafluoroantimonate,
1-(2-naphthoylmethyl)thioranium hexafluoroantimonate,
1-(2-naphthoylmethyl)thioranium trifluoromethanesulfonate,
4-hydroxy-1-naphthyldimethylsulfonium hexafluoroantimonate,
4-hydroxy-1-naphthyldimethylsulfonium trifluoromethanesulfonate, and the like.
(2) Organic Halogen Compounds
2-methyl-4,6-bis(trichloromethyl)-1,3,5-triazine,
2,4,6-tris(trichloromethyl)-1,3,5-triazine,
2-phenyl-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-chlorophenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(benzo[d][1,3]dioxolane-5-yl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(3,4,5-trimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(3,4-dimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(2,4-dimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(2-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-butoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,
2-(4-penttyloxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine, and the like.
(3) Sulfone Compounds
diphenyl disulfone,
di-p-tolyl disulfone,
bis(phenylsulfonyl)diazomethane,
bis(4-chlorophenylsulfonyl)diazomethane,
bis(p-tolylsulfonyl)diazomethane,
bis(4-tert-butylphenylsulfonyl)diazomethane,
bis(2,4-xylylsulfonyl)diazomethane,
bis(cyclohexylsulfonyl)diazomethane,
(benzoyl)(phenylsulfonyl)diazomethane, and the like.
(4) Sulfonate Compounds
1-benzoyl-1-phenylmethyl p-toluenesulfonate (common name: benzoin tosilate),
2-benzoyl-2-hydroxy-2-phenylethyl-p-toluenesulfonate (common name: xcex1-methylolbenzoin tosilate),
1,2,3-benzenetriyl trismethanesulfonate,
2,6-dinitrobenzyl p-toluenesulfonate,
2-nitrobenzyl p-toluenesulfonate,
4-nitrobenzyl p-toluenesulfonate,
N-(trifluoromethylsulfonyloxy)phthalimide,
N-(trifluoromethylsulfonyloxy)-5-norbornene-2,3-dicarboxyimide,
N-(trifluoromethylsulfonyloxy)naphthalimide,
N-(10-camphorsulfonyloxy)naphthalimide, and the like.
In addition, in the chemical amplification type resist utilizing a catalytic action of an acid generated from an acid generator, when a period from the patterning exposure to the post exposure bake is prolonged, a deterioration of performance by inactivation of the acid is generally caused. In order to avoid such inactivation of the acid caused by standing after the irradiation with radiation, it is known that a nitrogen-containing basic organic compound should be used as a quencher. In the present invention, use of a nitrogen-containing basic organic compound as a quencher is also effective for reducing the temperature dependence of post exposure bake and inhibiting the reaction in the unexposed part by a reduction of diffusion of the acid in order to improve stability. Specific examples of the nitrogen-containing basic organic compound include compounds represented by the following formulae: 
wherein R21, R22, R23, R24 and R25 independently represent hydrogen, an alkyl which may be optionally substituted with a hydroxyl group, a cycloalkyl, an aryl or an alkoxy and A represents an alkylene, carbonyl or imino. The alkyl and alkoxy represented by R21 to R25 may be groups having about 1 to 6 carbon atoms. The cycloalkyl may be a group having about 5 to 10 carbon atoms. The aryl may be a group having about 6 to 10 carbon atoms. The alkylene represented by A may be a group having about 1 to 6 carbon atoms and may be a straight chain or a branched chain.
In the resist composition of the present invention, amount of the alkali-soluble resin is preferably within a range of about 50 to 95% by weight, more preferably about 70 to 95% by weight, amount of the cross-linking agent is preferably within: a range of about 0.1 to 30% by weight, amount of the N-substituted succinimide compound of the formula (I) is preferably within a range of about 1 to 30% by weight, more preferably about 2 to 20% by weight, and amount of an acid generator other than the N-substituted succinimide compound is preferably within a range of about 0.5 to 20% by weight, based on the total solid content in the composition. When the amount of the cross-linking agent is too small, the effect by the cross-linking after the radiation irradiation and post exposure bake becomes insufficient. On the other hand, when the amount is too large, the fundamental property, such as resolution, may be lowered. Amount of the novolak resin having a weight average molecular weight of 900 or less optionally used as a part of the alkali-soluble resin is preferably within a range of about 5 to 50% by weight, based on the total solid content in the composition. The amount of such a lower molecular weight novolak resin is a part of the amount of the alkali-soluble resin. Amount of the nitrogen-containing basic organic compound optionally used as a quencher is preferably within a range of about 0.01 to 1% by weight, based on the total solid content in the composition. The resist composition may also contain, if necessary, a small amount of various additives commonly used in this field such as a resin other than the above-described alkali-soluble resin or dye.
A resist solution is prepared by dissolving the above-described ingredients in a solvent. The solvent used here may be anyone that dissolves all the ingredients, has an appropriate drying rate and gives a uniform and smooth film after evaporation of the solvent, and may be one commonly used in this field. Examples of the solvent include glycol ether esters such as ethyl cellosolve acetate, methyl cellosolve acetate, propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; glycol ethers such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether and propylene glycol monoethyl ether; esters such as ethyl lactate, butyl acetate, amyl acetate and ethyl pyruvate; ketones such as methyl amyl ketone and cyclohexanone; and cyclic esters such as xcex3-butyrolactone. These solvents may be used independently or as a mixture of two or more. The amount of the solvent may be adjusted so that, for example, the total solid concentration in the resist solution is about 5 to 50% by weight, considering the applicability, etc.
The negative working resist composition prepared in this manner is applied on a substrate such as silicon wafer according to the conventional manner, such as spin coating, to form a resist film. The film is then subjected to exposure for patterning. The exposure for patterning is carried out using a lower wavelength visible light or near ultraviolet rays such as g-ray of a wave length: 468 nm, i-ray of a wave length: 365 nm; far ultraviolet rays such as KrF eximer laser of a wave length: 248 nm and ArF eximer laser of a wave length: 193 nm; vacuum ultraviolet rays such as F2 eximer laser; soft X-ray of a wave length: 13 nm; electron beams; X-ray and so on. After the exposure for patterning, the film is subjected to the post exposure bake to cause the cross-linking reaction and developed with an alkaline developer. The alkaline developer may be of various kinds used in this field. Examples of the developer generally used include aqueous solution of tetramethyl ammonium hydroxide or (2-hydroxyethyl)trimethyl ammonium hydroxide (common name: choline).